5.1 HOW PLASTIC (FORMED-IN) INTERLOCKS WORK

There are applications for which mechanical joining is needed and preferred over processes that accomplish joining by creating atomic-level bonding (e.g., adhesive bonding or welding). Furthermore, for some of these applications, it is preferable to use integral features of the parts themselves for accomplishing the needed attachment and interlocking, but, for one reason or another, it is not feasible or practical to create those features in the detail parts during their fabrication prior to their assembly. For these applications, forming in (i.e., creating) the locking features once the parts of the intended assembly are in their proper relative positions, orientations, and alignments is preferable. For such applications, plastic formed-in integral mechanical attachments or interlocks are the answer.

Plastic (formed-in) integral mechanical attachments or plastic interlocks possess two differentiating characteristics compared to rigid and elastic integral mechanical attachments or interlocks. First, while their use for joining is planned by the designer, no particular geometric features are generally designed into the detail parts and, absolutely, no features capable of accomplishing actual locking are designed in or created prior to full part assembly. At most, in some forms of plastic interlocking, certain geometric features are designed into the detail parts that will allow a plastic interlock to be created by an additional and quite specific fabrication or processing operation. The second characteristic that distinguishes plastic interlocks from rigid or elastic interlocks is that the mating part being brought into appropriate intimate contact with the base...